Preparation method of sulfur-modified biochar and application of sulfur-modified biochar in selective removal of thallium in wastewater

Abstract

The invention provides a preparation method of sulfur modified biochar and application of the sulfur modified biochar in selective thallium removal in wastewater, and relates to the technical field of sewage treatment. The preparation method of the sulfur-modified biochar comprises the following steps: removing impurities from biomass, and drying; the dried biomass is sequentially subjected to ball-milling crushing and screening, and biomass powder is obtained; the obtained biomass powder is placed in a nitrogen atmosphere for a pyrolytic reaction, and the charcoal is obtained after cooling. The biochar has excellent adsorption performance on monovalent thallium (Tl < + >) in thallium-containing wastewater. According to the alfalfa biochar provided by the invention, the maximum adsorption rate of monovalent thallium (Tl < + >) in thallium-containing wastewater can be 99%, and the thallium content in the treated wastewater is lower than the national standard (lt); meanwhile, in the presence of coexisting ions, the adsorbent also has good adsorption performance (the experimental result is 95% or above). The preparation method is simple to operate, simple in equipment and low in cost.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to a method for preparing sulfur-modified biochar and its application in selectively removing thallium in wastewater. Background Art

[0002] Thallium is a companion element and rarely forms minerals on its own. It mostly exists as a dispersed isomorphous impurity (isomorphous substitution form) in sulfur-containing minerals of metals such as lead, zinc, iron, and copper, and lithium minerals (such as lepidolite, spodumene, etc.). Therefore, thallium-containing wastewater is inevitably produced during the mining process.

[0003] Thallium is extremely toxic to humans, exceeding the toxicity of common heavy metals like lead, cadmium, and mercury, and four times that of arsenic (As₂O₃). Its median lethal dose (LD50) is 10-15 mg / kg. Thallium is a non-essential trace element that can enter and accumulate in the human body through drinking water, food, and breathing. Its compounds are mutagenic, carcinogenic, and teratogenic, causing a variety of diseases, including esophageal cancer, liver cancer, and colorectal cancer, posing a significant threat to human health. Currently, chemical treatment methods, such as sedimentation and flocculation, are the most commonly used methods for treating industrial wastewater in China. While these methods can achieve standard discharge, they require large amounts of chemical reagents, are costly, and can cause secondary pollution. Other methods include electrolysis, but these methods are costly. Therefore, exploring lower-cost alternatives is both necessary and valuable.

[0004] In recent years, biochar has provided a new approach to the adsorption and removal of thallium in wastewater due to its high efficiency, economy and environmental protection, and has attracted increasing attention. For example, patent CN 113603180A discloses a method for preparing biochar, which comprises the following steps: (1) biomass pretreatment: drying sugarcane bagasse, grapefruit peel or banana peel and grinding and crushing them into biomass powder; (2) carbonization: placing the biomass powder obtained in step (1) in a ceramic ark, placing it in a tubular resistance furnace, heating it to 500°C at a rate of 5°C / min in an oxygen-free environment, and calcining it at a constant temperature for 1 hour to obtain the biochar; the biochar prepared by the method has a high adsorption capacity for thallium (Tl 3+ ) has high adsorption efficiency, simple process and low preparation cost. However, the main components present in most water bodies and wastewater are monovalent thallium (Tl + ), which has a stronger mobility than trivalent thallium (Tl 3+ ) and treats thallium trivalent (Tl 3+ Therefore, it is more difficult to explore suitable biochar materials and modification methods for removing monovalent thallium (Tl + ) is of great significance.

[0005] Those skilled in the art readily understand that biochar preparation temperature, time, and biomass feedstock are key factors influencing its structure and properties. Therefore, the effects of different biomass selection, temperature, heating time, and modification methods on the biochar's pore structure, specific surface area, functional groups, and electronic structure, and thus its adsorption and catalytic properties, are unpredictable. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention provides a method for preparing sulfur-modified biochar and its application in selectively removing thallium from wastewater. The biochar uses alfalfa / bamboo as raw materials to selectively remove thallium (Tl + ) has excellent adsorption properties.

[0007] Specifically, the present invention provides a method for preparing sulfur-modified biochar, comprising the following steps:

[0008] (1) removing impurities from the biomass and drying it;

[0009] (2) subjecting the biomass dried in step (1) to ball milling and screening in sequence to obtain biomass powder;

[0010] (3) placing the biomass powder obtained in step (2) in a nitrogen atmosphere for pyrolysis reaction, and obtaining the biochar after cooling.

[0011] Preferably, in step (1), the biomass is alfalfa or bamboo, both of which are biomass agricultural and forestry wastes or agricultural and forestry wastes after soil remediation.

[0012] Preferably, in step (1), the impurity removal is to wash the biomass with water to remove soil and other soluble impurities, and the drying is to dry in an oven at 50-70° C. for 10-15 h.

[0013] Preferably, in step (2), the powder is sieved to obtain a powder with a particle size of 0.075-0.25 mm.

[0014] Preferably, in step (3), the heating rate is 5-15°C / min, the pyrolysis temperature is 500-900°C, and the pyrolysis temperature is kept at the pyrolysis temperature for 0.5-4 h.

[0015] Preferably, in step (3), a pore-forming agent and a sulfur source are added to the biomass powder, followed by pyrolysis.

[0016] Preferably, in step (3), the pore-forming agent is selected from at least one of potassium chloride, potassium nitrate, potassium carbonate, and potassium bicarbonate, and the sulfur source is selected from at least one of sulfur powder, thiourea, ammonium thiocyanate, sodium lignin sulfonate, and sodium thiosulfate. By selecting a suitable pore-forming agent, the present invention can control the size (i.e., pore diameter) distribution and shape of the pores. The pore structure (increased specific surface area) and defective active sites generated by the pore-forming agent can improve the adsorption capacity of the adsorbent for thallium ions. The addition of the sulfur source can form new sulfur-containing functional groups, which have a specific chemical adsorption effect when adsorbing thallium ions.

[0017] Preferably, in step (3), based on the mass of the biomass powder being 100%, the amount of the pore-forming agent added is 5-15% of the biomass powder, and the amount of the sulfur source added is 20-50% of the biomass powder.

[0018] Excessive amounts of pore-forming agents can clog the pores within the biochar, causing the structure to collapse or collapse. At the same time, excessive additions can loosen the biochar's structure, reducing its overall specific surface area and, in turn, reducing the number of adsorption sites and lowering adsorption performance. When insufficient amounts of pore-forming agents are added, the number of pores formed is limited, and the specific surface area, porosity, and defectivity of the biochar cannot be effectively increased, resulting in fewer adsorption sites. Excessive amounts of sulfur sources can clog some of the biochar's pores, reducing the number of adsorption sites and lowering the biochar's adsorption performance. When insufficient amounts of sulfur sources are added, the biochar cannot be effectively modified, and sulfur-containing functional groups cannot be fully introduced.

[0019] The present invention also provides sulfur-modified biochar prepared by the method, and the use of the biochar for selectively removing thallium in wastewater, comprising the following steps:

[0020] (1) Adjust the temperature of thallium-containing wastewater to 10-45°C;

[0021] (2) Adding the biochar to thallium-containing wastewater.

[0022] Preferably, in step (1), the pH of the wastewater is 5.00-11.00, preferably 6.50; the thallium content in the wastewater is 0.5-10 mg / L, and the thallium in the wastewater is monovalent thallium (Tl + ), pH 5.00-11.00.

[0023] Preferably, in step (2), the amount of biochar added is 0.2-2 g / L, preferably 0.5 g / L; the stirring speed is 100-200 r / min, and the adsorption time is 5-60 min, preferably 30 min.

[0024] In one embodiment of the present invention, when the pH of thallium-containing wastewater is 6.90 and the temperature is 25°C, the alfalfa biochar pyrolyzed at 600°C can better achieve the monovalent thallium (Tl + ) removal. When the thallium-containing wastewater and the biochar were mixed for 30 minutes, an adsorption rate of over 99% was achieved. Furthermore, when the bamboo biochar was mixed with the thallium-containing wastewater for 30 minutes, an adsorption rate of over 95% was achieved.

[0025] Compared with the prior art, the present invention has the following beneficial properties:

[0026] The present invention provides a method for preparing sulfur-modified biochar and its application in selectively removing thallium from wastewater. The biochar is effective for removing monovalent thallium (Tl + ) has excellent adsorption performance. The alfalfa biochar provided by the present invention can achieve the treatment of monovalent thallium (Tl + ) with an adsorption rate of up to 99%. Thallium levels in treated wastewater are below the national standard (<5 μg / L). Furthermore, it exhibits excellent adsorption performance in the presence of coexisting ions (experimental results show a rate above 95%). The preparation method is simple, requires minimal equipment, and is low-cost. For biochar with inherently poor adsorption properties, additional pore creation and sulfur doping can enhance its adsorption performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0028] Figure 1 The alfalfa biochar (BC-500, BC-600, BC-700, BC-800, BC-900) prepared under different pyrolysis temperature conditions in Example 1 of the present invention is used to analyze the effect of thallium monovalent (Tl + ) of the adsorption performance diagram.

[0029] Figure 2 The alfalfa biochar (BC-600) in Example 2 of the present invention is subjected to different pH conditions to measure the effect of monovalent thallium (Tl + ) of the adsorption performance diagram.

[0030] Figure 3 The alfalfa biochar (BC-600) in Example 3 of the present invention is subjected to different cationic conditions to treat monovalent thallium (Tl + ) of the adsorption performance diagram.

[0031] Figure 4 The alfalfa biochar (BC-600) in Example 4 of the present invention is used to determine the effect of thallium monovalent (Tl + ) of the adsorption kinetics curve.

[0032] Figure 5 The alfalfa biochar (BC-600) in Example 5 of the present invention is subjected to the monovalent (Tl + ) of the adsorption performance diagram.

[0033] Figure 6 These are the XRD patterns of alfalfa biochar (BC-600) before and after adsorption.

[0034] Figure 7 FTIR images of alfalfa biochar (BC-600) before and after adsorption.

[0035] Figure 8 The bamboo biochar with different pore-forming agent addition amounts has a significant effect on the thallium (Tl + )’s adsorption performance diagram;

[0036] Figure 9 The effect of bamboo biochar on thallium (Tl + )’s adsorption performance diagram;

[0037] Figure 10 The bamboo biochar (BBC-700) is used to treat monovalent thallium (Tl + ) of the adsorption performance diagram. DETAILED DESCRIPTION

[0038] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0039] Example 1

[0040] A method for preparing alfalfa biochar and its application in removing thallium from wastewater, specifically using alfalfa biochar to remove monovalent thallium (Tl + ) is subjected to adsorption treatment, comprising the following steps:

[0041] 25 mg of alfalfa biochar (BC-500, BC-600, BC-700, BC-800, BC-900) prepared at different pyrolysis temperatures were weighed and added into 50 mL of Tl + The solution (the initial pH value of the solution is 6.90) was shaken for 30 minutes to complete the removal of thallium in the water.

[0042] Immediately after the reaction, 3 mL of the supernatant was collected with a syringe, filtered through a 0.45 μm filter, placed in a 5 mL centrifuge tube, and stored with 200 μL of 1:1 nitric acid. Two parallel experiments were performed for each group of materials. The thallium concentration in the solution was determined by ICP, and the amount of thallium adsorbed was calculated.

[0043] In this embodiment, the alfalfa biochar used is prepared by pyrolysis of alfalfa, comprising the following steps:

[0044] (1) Impurity removal: Place alfalfa in 30°C water, stir, and centrifuge at 3000 r / min to remove impurities;

[0045] (2) Drying: Place the cleaned alfalfa in an oven at 60°C and dry for 12 hours;

[0046] (3) Sieving: ball-mill the dried alfalfa and sieve to obtain a powder with a particle size of 0.1-0.15 mm;

[0047] (4) Pyrolysis: The sieved powder was pyrolyzed at 600°C at a heating rate of 10°C / min for 1 hour, and then naturally cooled to room temperature. After sieving, the biochar material required by the present invention was obtained.

[0048] In this embodiment, the preparation method of alfalfa biochar (BC-500) is basically the same as the preparation method of alfalfa biochar (BC-600), with the only difference being that the pyrolysis temperature for preparing BC-500 is 500°C.

[0049] In this embodiment, the preparation method of alfalfa biochar (BC-700) is basically the same as the preparation method of alfalfa biochar (BC-600), with the only difference being that the pyrolysis temperature for preparing BC-700 is 700°C.

[0050] In this embodiment, the preparation method of alfalfa biochar (BC-800) is basically the same as the preparation method of alfalfa biochar (BC-600), with the only difference being that the pyrolysis temperature for preparing BC-800 is 800°C.

[0051] In this embodiment, the preparation method of alfalfa biochar (BC-900) is basically the same as the preparation method of alfalfa biochar (BC-600), with the only difference being that the pyrolysis temperature for preparing BC-900 is 900°C.

[0052] Figure 1 The alfalfa biochar (BC-500, BC-600, BC-700, BC-800, BC-900) prepared under different pyrolysis temperature conditions in Example 1 was used to analyze the effect of thallium monovalent on the thallium monovalent. +) adsorption performance diagram. From the experimental results, the alfalfa biochar prepared at different pyrolysis temperatures has a good adsorption performance on monovalent thallium (Tl + ) showed significant differences in adsorption performance. At a pyrolysis temperature of 600°C, the biochar achieved a maximum thallium removal rate of 99.75%. As the pyrolysis temperature increased, the removal rate gradually decreased, reaching 97.85% at 700°C, 98.57% at 800°C, and 96.24% at 900°C, respectively.

[0053] From the chemical principles of the pyrolysis process, it is clear that as the pyrolysis temperature increases, the organic matter in alfalfa undergoes complex pyrolysis reactions. At lower temperatures, the pore structure and surface functional groups of biochar are not fully developed, limiting its adsorption capacity. When the temperature rises to 600°C, the pore structure of the biochar is optimized, the specific surface area increases, and the content and activity of surface functional groups (such as carboxyl and phenolic hydroxyl groups) reach an ideal state. These factors collectively promote the adsorption of thallium ions. However, as the pyrolysis temperature continues to rise, some functional groups in the biochar may undergo decomposition or condensation reactions, resulting in a decrease in their activity. Excessively high temperatures can also cause the pore structure of the biochar to collapse or sinter, reducing its specific surface area and adsorption performance.

[0054] This indicates that the alfalfa biochar (BC-600) produced by the present invention achieves a thallium removal rate of 99%, completely adsorbing thallium (residual Tl <5 μg / L), demonstrating the excellent adsorption properties of the alfalfa biochar. BC-600 exhibits optimal adsorption performance under the conditions of an initial pH of 6.90, a pyrolysis temperature of 600°C, and an alfalfa biochar dosage of 0.5 g / L, achieving a thallium removal rate of nearly 100% within 30 minutes.

[0055] Example 2

[0056] A method for preparing alfalfa biochar and its application in removing thallium from wastewater, specifically using alfalfa biochar to remove monovalent thallium (Tl + ) is subjected to adsorption treatment, comprising the following steps:

[0057] Take 5 portions of 50 mL of Tl + The solution was adjusted to pH 3.00, 5.00, 7.00, 9.00, and 11.00, respectively, and 25 mg of alfalfa biochar (BC-600) prepared in Example 1 was added. The mixture was shaken for 30 min to ensure that the adsorption equilibrium was reached, thereby completing the removal of thallium from the water.

[0058] Immediately after the reaction, 3 mL of the supernatant was collected with a syringe, filtered through a 0.45 μm filter, placed in a 5 mL centrifuge tube, and stored with 200 μL of 1:1 nitric acid. Two parallel experiments were performed for each group of materials. The thallium concentration in the solution was determined by ICP, and the amount of thallium adsorbed was calculated.

[0059] Figure 2 The alfalfa biochar (BC-600) in Example 2 of the present invention is subjected to different pH conditions to measure the effect of monovalent thallium (Tl + ) adsorption performance diagram. Figure 2 It can be seen that biochar has good adsorption performance under weakly acidic, neutral and alkaline conditions (Tl + The removal rates of Tl were between 93.48% and 96.10%, and when the initial pH of the thallium solution was 3, the removal rate of Tl + The adsorption performance of Tl is poor, which may be because: under acidic conditions, the adsorbent has a positive charge on the surface due to good protonation, which leads to the + Strong electrostatic repulsion is generated between the positive charges on the adsorbent surface. Therefore, the applicable pH range of the entire reaction system is 5.00-11.00, and efficient removal of thallium (≥90%) can be achieved within 30 minutes.

[0060] Example 3

[0061] A method for preparing alfalfa biochar and its application in removing thallium from wastewater, specifically using alfalfa biochar to remove monovalent thallium (Tl + ) is subjected to adsorption treatment, comprising the following steps:

[0062] Take 5 portions of 50 mL of Tl + solution, adding K + 、Na + Mg 2+ and Ca 2+ , so that the concentrations of the above ions in the solution were 1 mM and 10 mM. 25 mg of alfalfa biochar (BC-600) prepared in Example 1 was added to each solution, and the mixture was shaken for 30 minutes to ensure that adsorption equilibrium was achieved, thereby completing the removal of thallium from the water.

[0063] Immediately after the reaction, 3 mL of the supernatant was collected with a syringe, filtered through a 0.45 μm filter, placed in a 5 mL centrifuge tube, and stored with 200 μL of 1:1 nitric acid. Two parallel experiments were performed for each group of materials. The thallium concentration in the solution was determined by ICP, and the amount of thallium adsorbed was calculated.

[0064] Figure 3The alfalfa biochar (BC-600) in Example 3 of the present invention is subjected to different cationic conditions to treat monovalent thallium (Tl + ) adsorption performance diagram. Figure 3 It can be seen that the BC-600 of the present invention has good applicability to most common inorganic cations, and the alfalfa biochar (BC-600) has good applicability.

[0065] Example 4

[0066] A method for preparing alfalfa biochar and its application in removing thallium from wastewater, specifically using alfalfa biochar to remove monovalent thallium (Tl + ) is subjected to adsorption treatment, comprising the following steps:

[0067] Weigh 25 mg of alfalfa biochar (BC-600) and add it to 50 mL of 1 mg / L Tl + The solution (the initial pH of the solution is 6.90) is shaken to complete the removal of thallium from the water.

[0068] During the adsorption reaction, 3 mL of supernatant was collected with a syringe at 5 min, 10 min, 15 min, 20 min, 30 min, 45 min, 60 min, and 90 min, respectively. The supernatant was filtered through a 0.45 μm filter and placed in a 5 mL centrifuge tube. 200 μL of 1:1 nitric acid was added for storage. A parallel experiment was performed for each group of materials. The thallium concentration in the solution was determined by ICP, and the amount of thallium adsorbed was calculated.

[0069] Figure 4 The alfalfa biochar (BC-600) in Example 4 of the present invention is used to determine the effect of thallium monovalent (Tl + ) adsorption kinetics curve. It can be seen that within the first 5 minutes of adsorption, there are a large number of available adsorption sites on the adsorbent surface, and the concentration of Tl⁺ in the solution is high, so a strong concentration gradient will be generated. In this case, the adsorption rate is very high, and the adsorbent can quickly capture Tl + .Depend on Figure 6 The fitting curves show that the pseudo-first-order kinetic and pseudo-second-order kinetic models of alfalfa biochar are very appropriate, and the pseudo-first-order kinetic and pseudo-second-order kinetic fitting coefficients R 2 Both are 0.999, and there is almost no difference between the two. This shows that at this concentration, the adsorption of thallium is a combination of physical adsorption and chemical adsorption. Figure 7 The FTIR test results show that alfalfa biochar has more oxygen-containing functional groups, which is conducive to the chemical adsorption of thallium by biochar.

[0070] Example 5

[0071] A method for preparing alfalfa biochar and its application in removing thallium from wastewater, specifically using alfalfa biochar to remove monovalent thallium (Tl + ) is subjected to adsorption treatment, comprising the following steps:

[0072] Weigh 25 mg of alfalfa biochar (BC-600) and add it to 50 mL of 1 mg / L Tl + The solution (the initial pH of the solution is 6.90) was shaken for 30 minutes to ensure that the adsorption equilibrium was reached and the removal of thallium in the water was completed.

[0073] Immediately after the reaction, 3 mL of the supernatant was collected with a syringe, filtered through a 0.45 μm filter, placed in a 5 mL centrifuge tube, and stored with 200 μL of 1:1 nitric acid. Two parallel experiments were performed for each group of materials. The thallium concentration in the solution was determined by ICP, and the amount of thallium adsorbed was calculated.

[0074] With the rapid development of industry, the discharge of thallium-containing wastewater has been increasing, posing a serious threat to the environment. In order to further explore the application potential of biochar in actual wastewater treatment, the present invention uses alfalfa biochar (BC-600) to treat the monovalent (Tl + ) was adsorbed, and the results are shown in Figure 5 , to evaluate its removal performance in complex water environments. The results showed that compared with the treatment performance under laboratory conditions, the removal rate of biochar in actual water bodies decreased slightly, but the overall decrease was small. This phenomenon may be attributed to the rich functional groups on the surface of biochar, which can adsorb thallium (Tl) in wastewater, thereby effectively removing the target pollutant. Therefore, biochar still has a high application value in actual wastewater treatment and provides a feasible solution for the treatment of thallium-containing wastewater.

[0075] Figure 6 The XRD patterns of alfalfa biochar (BC-600) before and after adsorption. As can be seen from the figure, KCl crystals exist before alfalfa biochar adsorption, and the KCl crystals disappear after adsorption, indicating that K + In Tl + The adsorption process was + Replaced by Tl + Replace K + The generated TlCl adheres to the surface of biochar and is adsorbed by biochar and removed from the aqueous solution.

[0076] Figure 7 The FTIR images of alfalfa biochar (BC-600) before and after adsorption are shown in the figure. -1 The peak is attributed to OH stretching; at a wave number of 2327.5 cm-1 The peak at wave number 1631.8 cm is attributed to the antisymmetric stretching vibration of CO2; -1 The peak is attributed to the stretching vibration of aromatic C=C and carboxylic acid C=O; the peak at wave number 1384.9 cm -1 、1352.1 cm -1 The peak at is attributed to the C-OH vibration of carboxylic acid. After the reaction, the stretching peak of OH and the C-OH vibration peak of carboxylic acid are significantly weakened, indicating that Tl + It replaces H and is then adsorbed by biochar and removed from the aqueous solution.

[0077] Example 6

[0078] A preparation method of bamboo biochar and its application in removing thallium from wastewater, specifically using bamboo biochar to remove monovalent thallium (Tl + ) is subjected to adsorption treatment, comprising the following steps:

[0079] Weigh 25 mg of bamboo biochar (BBC-700) and add it to 50 mL of Tl + The solution (the initial pH of the solution is 6.90) was shaken for 30 minutes to ensure that the adsorption equilibrium was reached and the removal of thallium in the water was completed.

[0080] Immediately after the reaction, 3 mL of the supernatant was collected with a syringe, filtered through a 0.45 μm filter, placed in a 5 mL centrifuge tube, and stored with 200 μL of 1:1 nitric acid. Two parallel experiments were performed for each group of materials. The thallium concentration in the solution was determined by ICP, and the amount of thallium adsorbed was calculated.

[0081] In this embodiment, the bamboo biochar used is prepared by pyrolysis of bamboo, comprising the following steps:

[0082] (1) Impurity removal: Place the bamboo in 30°C water, stir, and centrifuge at 3000 r / min to remove impurities;

[0083] (2) Drying: Place the bamboo after impurities removal in an oven at 60°C and dry for 12 hours;

[0084] (3) Sieving: ball-mill the dried bamboo and sieve out a powder with a particle size of 0.1-0.15 mm;

[0085] (4) Pyrolysis: The sieved bamboo powder, pore-forming agent, and sulfur source were uniformly mixed. The pore-forming agent was potassium bicarbonate, and its addition amount was 10% by weight of the bamboo powder. The sulfur source was sodium lignin sulfonate, and its addition amount was 50% by weight of the bamboo powder. The mixture was heated at a rate of 10°C / min and pyrolyzed at 700°C for 1 hour. The mixture was then naturally cooled to room temperature and sieved to obtain the biochar material BBC-700 required by the present invention.

[0086] This example also conducted comparative experiments: 1) direct pyrolysis of bamboo powder at the same temperature without the addition of a pore-forming agent or sulfur source; and 2) pyrolysis of bamboo powder with a pore-forming agent, potassium bicarbonate, at concentrations of 3%, 5%, 10%, 15%, and 20% of the bamboo powder mass, respectively, without the addition of a sulfur source. The mixture was pyrolyzed at 700°C at a heating rate of 10°C / min for 1 hour, then cooled to room temperature and sieved to obtain the biochar material of the present invention.

[0087] Depend on Figure 8 It can be seen that when the pore-forming agent is added at 3%, the biochar pore structure is imperfect and the adsorption sites are few, resulting in a low adsorption removal rate. When the pore-forming agent is added at 20%, the internal pores of the biochar are blocked or collapsed. At the same time, excessive addition may loosen the biochar structure, resulting in a decrease in its overall specific surface area, which in turn reduces the number of adsorption sites and lowers adsorption performance. Therefore, the addition of pore-forming agent should be controlled between 5% and 15%.

[0088] Based on the above, this example also conducted a comparative experiment. The pore-forming agent was potassium bicarbonate, and the pore-forming agent addition amount was 10% of the bamboo powder mass. The sulfur source was sodium lignin sulfonate, and its addition amount was 10%, 20%, 30%, 40%, and 50% of the bamboo powder mass, respectively. The mixture was heated at a heating rate of 10°C / min and pyrolyzed at 700°C for 1 hour. It was then naturally cooled to room temperature and sieved to obtain the biochar material required by the present invention. Figure 9 It can be seen that the amount of S source added should be controlled at 20%-50%.

[0089] Figure 10 The bamboo biochar (BBC-700) in Example 6 of the present invention is used to measure the monovalent thallium (Tl + ). The figure shows that the addition of a pore-forming agent and a sulfur source significantly improves the adsorption of thallium, from 52.39% to 96.24%. This demonstrates that the addition of sulfur (S) and a pore-forming agent during the pyrolysis process significantly enhances the adsorption performance of bamboo biochar. This modified biochar has broad application prospects in actual wastewater treatment, effectively reducing treatment costs and improving treatment efficiency.

[0090] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing sulfur-modified biochar, characterized in that: The steps include: (1) removing impurities from the biomass and drying it; (2) subjecting the biomass dried in step (1) to ball milling and screening in sequence to obtain biomass powder; (3) placing the biomass powder obtained in step (2) in a nitrogen atmosphere for pyrolysis reaction, and obtaining the biochar after cooling.

2. The method for preparing sulfur-modified biochar according to claim 1, wherein: In step (1), the biomass is alfalfa or bamboo.

3. The method for preparing sulfur-modified biochar according to claim 1, wherein: In step (1), the impurity removal is to wash the biomass with water, and the drying is to dry it in an oven at 50-70° C. for 10-15 h.

4. The method for preparing sulfur-modified biochar according to claim 1, wherein: In step (2), the powder is sieved to obtain a powder with a particle size of 0.075-0.25 mm.

5. The method for preparing sulfur-modified biochar according to claim 1, wherein: In step (3), the heating rate is 5-15°C / min, the pyrolysis temperature is 500-900°C, and the pyrolysis temperature is kept at 0.5-4 h.

6. The method for preparing sulfur-modified biochar according to claim 1, wherein: In step (3), a pore-forming agent and a sulfur source are added to the biomass powder, followed by pyrolysis; Preferably, the pore-forming agent is selected from at least one of potassium chloride, potassium nitrate, potassium carbonate, and potassium bicarbonate, and the sulfur source is selected from at least one of sulfur powder, thiourea, ammonium thiocyanate, sodium lignin sulfonate, and sodium thiosulfate.

7. The method for preparing sulfur-modified biochar according to claim 6, wherein: In step (3), based on the mass of the biomass powder being 100%, the amount of the pore-forming agent added is 5-15% of the biomass powder, and the amount of the sulfur source added is 20-50% of the biomass powder.

8. Use of the sulfur-modified biochar prepared by the method according to any one of claims 1 to 7 in selectively removing thallium from wastewater, characterized in that: The steps include: (1) Adjust the temperature of thallium-containing wastewater to 10-45°C; (2) Adding the biochar to thallium-containing wastewater.

9. The use according to claim 8, characterized in that In step (1), the pH of the wastewater is 5.00-11.00, preferably 6.50; the thallium content in the wastewater is 0.5-10 mg / L, and the thallium in the wastewater is monovalent thallium (Tl + ), pH 5.00-11.

00.

10. The use according to claim 8, characterized in that In step (2), the amount of biochar added is 0.2-2 g / L, preferably 0.5 g / L; the stirring speed is 100-200 r / min, and the adsorption time is 5-60 min, preferably 30 min.

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